1. Field of the Invention
The present invention relates to a composite polarizing plate capable of obtaining excellent visibility under a bright environment, reducing parallax, and thinning a liquid crystal display device, and to a liquid crystal display device using the composite polarizing plate.
2. Description of the Related Art
In a cellular phone, a plastic substrate (generally, acrylic plate) is generally placed above a liquid crystal display portion in order to impart durability and design characteristics. For an in-car display such as a car navigation system, a tablet PC frequently used for industry, a public display, and a multi-function cellular phone, a touch panel is placed on a surface of a display portion (for example, JP 2001-201741 A).
A front substrate, for example, a plastic substrate or a touch panel is normally fixed to a polarizing plate by a double-faced tape bonded to edge portion of the polarizing plate. A thickness of the double-faced tape is normally approximately 120 μm, and hence there is a problem that a total thickness of the liquid crystal display device increases. When the front substrate is used for the touch panel, in order to minimize a shock, a sponge of approximately 1,000 μm is used together with the double-faced tape, and hence the thickness further increases. Since only the edge portion is adhered by the double-faced tape, an air layer is formed between the polarizing plate and the front substrate. When the refractive index of air is approximately 1.0, a refractive index of a material, for example, polymer or glass, of the front substrate is approximately 1.4 to 1.7. Therefore, a refractive index difference between the air layer and the front substrate is large, and hence there is a problem that visibility under a bright environment is reduced by interface reflection of outside light.
Furthermore, it should be noted that a color filter layer of a liquid crystal cell normally acts as a screen. When the touch panel is used as the front substrate, input contact points correspond to a surface of the front substrate, but are provided at a distance from a surface of the liquid crystal cell serving as the screen. Therefore, there is a problem that parallax occurs.
Meanwhile, a touch panel using a plastic film as an insulating substrate has a problem that a Newton ring is generated. As a method of preventing the generation of the Newton ring, there has been known a technology of forming a satin finished surface on at least one of facing surfaces of an upper insulating substrate and a lower insulating substrate and further using a diffusion pressure-sensitive adhesive layer in combination with the satin finished surface (for example, JP 2004-127243). However, even when the touch panel described in JP 2004-127243 is used, parallax cannot be reduced.